This invention relates to a process for producing a material composed of a functional compound finely dispersed into a binder resin.
In the explanation in detail, this invention relates to a process for dispersing finely the compounds having various functions such as pigments having a coloring function, functional dyes having a photo-dichroism, magnetic materials having magnetic recording characteristics, ultra-violet absorbers and the like into a binder resin, in order to disperse the compounds in a binder resin faithfully to the primary particle size distributions that the compounds keeping inherently by destroying agglomeration of particles of the compounds to free individual particles.
In the another explanation in detail, this invention relates the so-called sub-micron dispersion technique which means the technique to obtain the dispersed particles having particle size distributions of less than 1 micron.
The material of an above compound dispersed into a binder resin is used in fields relating to high-tech apparatus such as an ink for ink jet, a paint or ink for color filter for flat display, a colorant for toner for a color-copying machine, a coating composition for a polarized light filter, an other intermediate material containing the functional compound finely dispersed for producing an electronic device and the like.
The method for dispersing the functional compound is broadly classified into the following two procedures (EUROPEAN INK MAKER, Apr. 27, 1994, Vol. 184, No. 4348, pages 52 to 53):
1) A procedure of dispersing a finely divided and dried compound. PA1 2) A procedure of dispersing a hydrous paste of a finely divided compound.
The procedure 1) is a general one which has heretofore been used, and the dispersing machines which have been often used include three roll mill, twin roll mill and high-speed dispersing machines in which a medium is used, for example, pebble mill, sand mill and the like, and recently further include dispersing machines for grinding in which a hard, fine material such as zirconium or the like is used as the medium. The fact is that using these machines, the functional compound is dispersed in a dispersing agent or a resin which has an affinity for the functional compound. According to this procedure, the operation is relatively simple, but in the dried compound, there coexist rough particles formed by agglomeration of the compound, so that in order to break the rough particles apart into the original finely divided particles, namely primary particles, it is actually unavoidable to make the dispersing step unnecessarily long or to carry out the dispersion using a very expensive dispersing machine at the sacrifice of a production speed. Moreover, the fact is that with some lots of the compound, the agglomerated particles cannot be broken apart into the original primary particles.
Whether or not the procedure 2) is higher in economical efficiency than the procedure 1) has long been discussed, and the procedure 2) has been adopted case by case. The procedure 2) comprises kneading with heat a resin as a binder, a dispersing agent having an affinity for the above compound as occasion demands, and a hydrous paste, namely a pressed cake, of the functional compound which has been filtrated to remove a large amount of water from the aqueous suspension of the finely divided and washed functional compound after having been chemically synthesized.
In this kneading process, a kneaded mixture release the water content by a phase separation and the above compound is dispersed in the binder resin.
In this kneading process, if necessary, the mixture to be kneaded may be kneaded under pressure applied by a plunger. As the recent technical level, an example is disclosed in U.S. Pat. No. 5,529,871; JP-A 4(1992)-39,671; JP-A 4(1992)-242,752; JP-A 6(1994)-130,724; and the like. This procedure uses a hydrous paste of the above compound, so that in almost all cases, no agglomerate of the compound coexists and the dispersion is relatively easy; however, it is disadvantageous in that a long period of time is required for removing water and much energy is consumed therefor. In addition, it is the fact that with the functional compound having an affinity for water, a long period of time is required for removing the water content.